Uptake and Subcellular Localization of Neurotransmitters in the Brain

Localization of putative transmitters in the hippocampal formation: with a note on the connections to septum and hypothalamus

Biochemical assays on microdissected samples, denervation studies, subcellular fractionation, and light and electron microscopic autoradiography of high affinity uptake have been performed to study the cellular localization of transmitter candidates in the rat hippocampal formation. High affinity uptake of glutamate and aspartate is localized in the terminals of several excitatory systems, such as the entorhino-dentate fibres (perforant path), mossy fibres (from granular cells) and pyramidal cell axons. Thus, in stratum radiatum and oriens of CA1, 85% of glutamate and asparate uptake and 40% of glutamate and aspartate content are lost after lesions of ipsilateral plus commissural fibres from CA3/CA4. Hippocampal efferents also take up aspartate and glutamate, since these activities are heavily reduced in the lateral septum and mamillary bodies after transection of fimbria and the dorsal fornix. The synthesis (by glutamic acid decarboxylase), content and high affinity uptake of gamma-aminobutyrate (GABA) are not reduced after lesions of these or other projection fibre systems. A localization in intrinsic neurons is confirmed by a selective loss of glutamic acid decarboxylase after local injections of kainic acid. Peak concentrations of the enzyme occur near the pyramidal and granular cell bodies, corresponding to the site of the inhibitory basket cell terminals, and in the outer parts of the molecular layers. Some 85% of glutamic acid decarboxylase is situated in 'nerve ending particles'. Acetylcholine synthesis (by choline acetyltransferase) disappears after lesions of septo-hippocampal fibres. Since 80% of the hippocampal choline acetyltransferase is in 'nerve ending particles', the characteristic topographical distribution of this enzyme should reflect the distribution of cholinergic septo-hippocampal afferents. Serotonin, noradrenaline, dopamine and histamine are located/synthesized in afferent fibre systems. Some monoamine-containing afferents to the hippocampal formation pass via the septal area, others via the amygdala. The hippocampal formation also contains nerve elements reacting with antibodies against neuroactive peptides, such as enkephalin, substance P, somatostatin and gastrin/cholecystokinin.

Influence of a 1 h immobilization stress on sleep states and corticotropin-like intermediate lobe peptide (CLIP or ACTH18-39, Ph-ACTH18-39) brain contents in the rat

A 1 h immobilization stress (IS) was imposed to rats at the beginning of the dark period, i.e., when the animals start to be active. The IS was accompanied by an intense polygraphic waking and followed, over 12 h of the dark period, by a significant rebound of slow-wave sleep (SWS, +17%) and paradoxical sleep (PS, +57%). In order to estimate the IS-related changes in the endogenous concentrations of corticotropin-like intermediate lobe peptide (CLIP, ACTH18-39) and related compounds, a specific radioimmunoassay (RIA) was used. Assays performed in cerebral biopsies taken from arcuate (AN) and raphe dorsalis (nRD) nuclei led to the obtention of 2 main immunoreactive peaks, corresponding to CLIP and its phosphorylated form Ph-CLIP. Just after end of the IS and within the nRD. Ph-CLIP immunoreactivity increased by about 95%. Four hours later, i.e., when PS rebound was maximal, a 37% increase in Ph-CLIP immunoreactivity was measured in the AN. These observations have never been described before. In the blood, at the end of the restraint, CLIP/ACTH1-39 total immunoreactivity was increased by 330%. It returned to baseline level 4 h later. Blood concentration of corticosterone was also increased by 56% at the end of the IS and was close to baseline level 4 h later. Data reported here indicate that the IS first triggers an increase in Ph-CLIP within the nRD. Since the nRD contains sleep permissive components, this increase might be determinant for the SWS and PS rebound induction. The changes observed in the blood as regards CLIP/ACTH1-39 total immunoreactivity and corticosterone concentration testify to the efficacy of the IS and are part of the conventional picture accompanying such a situation. Finally, the increase in Ph-CLIP, occurring in the AN 4 h after the end of the restraint, might be part of the restorative processes necessary to compensate the stress overshoot.

Autoradiographic studies on the uptake of 3H-dopamine by neurons and astrocytes in explant and primary cultures of rat CNS: effects of uptake inhibitors

The cellular localization of the uptake of 3H-dopamine was studies in explant and primary cultures from various regions of rat central nervous system by means of autoradiography. In explant cultures of substantia nigra, 3H-dopamine was taken up by cell bodies and processes of many neurons. In cultures from striatum, cerebellum and spinal cord, neuronal cell bodies were not labelled, whereas outgrowing nerve fibres revealed intense uptake of the monoamine. Uptake of 3H-dopamine by neurons was Na(+)- and temperature-dependent, suggesting an active uptake mechanism. In explant cultures, astrocytes did not accumulate 3H-dopamine, whereas in primary cultures, which were prepared from the same regions of rat central nervous system as the explant cultures, astrocytes also revealed uptake of this monoamine. The intensity of labelling was dependent on the incubation time. Little uptake of 3H-dopamine was observed after an incubation time of 5 min and only after 10-15 min did the astrocytes show moderate labelling. Uptake of 3H-dopamine by astrocytes was not Na(+)- and temperature-dependent, indicating that glial cells do not possess an active uptake mechanism for this monoamine. This is consistent with biochemical investigations by other laboratories, demonstrating that astrocytes accumulate 3H-dopamine by a facilitated diffusion system. Addition of the uptake inhibitors nomifensine or GBR 12909 to explant cultures markedly reduced or inhibited uptake of 3H-dopamine by neurons at a concentration of 10(-6) M. In contrast, accumulation of 3H-dopamine by astrocytes in primary cultures was only slightly affected by nomifensine at 10(-6) M. At the highest concentration used (10(-5) M), nomifensine also blocked the uptake of 3H-dopamine by astrocytes. Our finding that GBR 12909 almost completely inhibited the uptake of 3H-dopamine by astrocytes already at 10(-6) M suggests that this compound is a more potent inhibitor of the glial uptake of dopamine than nomifensine.

Effects of tianeptine, sertraline and clomipramine on brain serotonin metabolism: a voltammetric approach in the rat

Tianeptine is a substance enhancing the serotonir uptake while sertraline and clomipramine inhibit it. By means of 5-hydroxyin-doleacetic acid (5-HIAA) voltammetric measurements, this study investigated their influence on serotonin metabolism which depends mainly upon the activity of monoamine oxidase type A. After tianeptine injection the 5-HIAA signal increased by about 60%. This effect was maintained when the animals were pre-treated with MDL 72145 (an inhibitor of monoamine oxidase type B) but reduced when clorgyline (an inhibitor of monoamine oxidase type A) was administered after tianeptine. Administration of sertraline or clomipramine reduced the 5-HIAA signal by about 30-50%, whether the animals were pre-treated with MDL 72145 or not. It is to be concluded that tianeptine, sertraline and clomipramine can regulate the 5-HT fraction present in the synaptic cleft, not only by acting at the level of the serotoninergic neurons, but also by favoring or reducing the access of the amine to monoamine oxidase type A which is synthesized within non-serotoninergic neurons and glial cells.

Autoradiographic studies on the uptake of 3H-noradrenaline and 3H-serotonin by neurones and astrocytes in explant and primary cultures of rat CNS: effects of antidepressants

Autoradiographic studies were made on the uptake of 3H-noradrenaline and 3H-serotonin in explant cultures and primary astrocyte cultures from various regions of rat central nervous system (cortex, cerebellum, locus coeruleus, nucleus raphé, spinal cord). In explant cultures from locus coeruleus and nucleus raphé cell bodies and processes of many neurones revealed intense labelling by 3H-noradrenaline and 3H-serotonin, respectively. In cultures from cortex, cerebellum and spinal cord the cell bodies of neurones did not show labelling by the monoamines but many nerve fibres in the outgrowth zone had taken up 3H-noradrenaline and 3H-serotonin. Astrocytes in explant cultures did not take up 3H-noradrenaline and 3H-serotonin whereas astrocytes in primary cultures showed heavy uptake of both monoamines. In contrast, amino acid transmitters such as 3H-GABA and 3H-glutamate were accumulated by astrocytes in explant as well as in primary cultures. Uptake of both 3H-noradrenaline and 3H-serotonin by neurones and astrocytes was considerably reduced or inhibited in Na(+)-free incubation medium or at low temperature, suggesting an active uptake mechanism. Addition of the antidepressants maprotiline and (+)oxaprotiline inhibited the uptake of 3H-noradrenaline by neuronal cell bodies and fibres in explant cultures and by astrocytes in primary cultures. The uptake of 3H-serotonin by neurones and astrocytes was blocked by citalopram and paroxetine. Our studies demonstrate that astrocytes in primary cultures are able to actively take up 3H-noradrenaline and 3H-serotonin whereas there was no uptake of monoamines into astrocytes in explant cultures, suggesting that there is a difference between astrocytes in different culture systems (explant cultures vs primary cultures) with respect to the uptake of monoamine transmitters.

[3H]Nisoxetine binding sites in the cat brain: an autoradiographic study

The binding of [3H]nisoxetine, a selective inhibitor of the high-affinity noradrenaline uptake sites, was studied on frontal frozen sections of the cat brain. The highest densities in autoradiographic signal were observed in the nucleus locus coeruleus and its ascending pathways, in the area postrema and in the dorsal part of the inferior olive, the pontine nuclei, the raphe nuclei, the colliculi, the periventricular and lateral areas of the hypothalamus, the suprachiasmatic nucleus, the nucleus accumbens and the olfactory bulb. A moderately high concentration of binding sites was observed in the hippocampal formation, especially in the molecular layer of Ammon's horn, in the superficial layers of the entorhinal cortex and in the indusium griseum. Binding sites were visualized in all the subdivisions of the neocortex. The highest density of binding was generally detected in the outer edge of the superficial layer I. In some cortical areas, especially in the visual cortex, labeling with a prevalent laminar distribution in the superficial layers I-III and in the deep layers V-VI was clearly observed. Moderate to low densities of binding sites were seen in most other areas of the brain except in the white matter, the caudate nucleus and putamen, which were devoid of labeling. Overall these findings indicate a good correlation between the distribution of [3H]nisoxetine binding sites and the noradrenergic systems. Furthermore, data suggest that in several areas, high-affinity noradrenaline reuptake mechanisms could play an important role in local interactions between the noradrenergic system and the other monoaminergic systems.

Evidence for a sleep-promoting influence of stress

In the present review the data supporting the existence at the central level of a stress-sleep relation are reported and discussed. An immobilization stress of 1 or 2 hour(s) is accompanied by a marked polygraphic waking and followed by a significant sleep rebound concerning mainly paradoxical sleep (PS). During the restraint, an important release of 5-hydroxyindoles [5-OHles, a good index of serotonin (5-HT) release] occurs in the basal hypothalamus (BH). This release, produced by the nerve endings originating from the nucleus raphe dorsalis (nRD), might secondarily influence the release and/or the synthesis of hypnogenic substances directly involved in the sleep rebound production. Corticotropin-like intermediate lobe peptide (CLIP, or ACTH18-39) is a peptide possessing hypnogenic properties and derived from proopiomelanocortin (POMC) whose perikarya are contained within the BH (arcuate nucleus). The POMC nerve endings impinge on the nucleus raphe dorsalis, a structure containing sleep permissive components upon which CLIP acts to trigger sleep. It remains to be defined how the activity of the neuronal loop described above is impaired under chronic stress conditions.

A model of the sodium dependence of dopamine uptake in rat striatal synaptosomes

Initial velocity of uptake of dopamine (DA) has been measured in rat striatal synaptosomes as a function of both [DA] and [Na]. Carrier mediated uptake is totally dependent on external sodium. The data were fitted to a rapid equilibrium model which has been found in previous studies to fit, with appropriate simplification, uptake data for glutamate, GABA, and choline in several brain regions under varying conditions. This model also gives a good fit to the dopamine data. The minimal best fit simplification of this model allows for DA uptake along with two sodium ions and predicts that apparent maximal velocity of uptake should increase with [Na], while the Michaelis-Menten constant should decrease. The minimal best fit model for DA, and a number of kinetic parameters which quantitate the model, are compared to those for the GABA, glutamate, and choline transporters. The results are consistent with a symmetrical, rapid equilibrium model, which has been presented previously for other neurotransmitters and precursors (18). This model offers a unifying basis for understanding the sodium and membrane potential dependence of neurotransmitter transport and the possible participation of transporters in depolarization induced release throughout the CNS.

Neurotransmitter transporters (plus): a promising new gene family

Neurotransmitter transporter genes encode proteins with 12 putative transmembrane regions, which mediate Na(+)-dependent reaccumulation of released neurotransmitters into presynaptic terminals and are the sites of action of important abused and therapeutic drugs. Studies of these genes show promise for improving our understanding of transport mechanisms and modes of drug action, and may even uncover previously unanticipated neurotransmitters.

Dopamine transporter: expression in Xenopus oocytes

Xenopus oocytes can express biologically relevant transport activity after injection of mRNAs encoding several carrier molecules. mRNA from PC12 cells, as well as transcripts from a rat ventral midbrain library, can be expressed in these oocytes and allow them to display pharmacologically specific dopamine uptake. mRNA-injected oocytes incubated with tritiated dopamine contain tritiated dopamine and metabolites; lower amounts of radiolabeled dopamine and more radiolabeled metabolites are found in oocytes co-incubated with cocaine or in water-injected oocytes. Tritiated dopamine uptake into mRNA-injected oocytes is time, sodium, and temperature dependent. It is blocked by cocaine and mazindol, but not by haloperidol. It is not found after injection of mRNA from other brain regions. A size-selected rat midbrain library constructed in the plasma vector pCDM8 yields mRNA transcripts whose injection into oocytes causes cocaine-blockable [3H]dopamine uptake. These findings provide an assay for purification of the dopamine transporter cDNA by sib selection techniques.

Actions of cocaine on rat nucleus accumbens neurones in vitro

1. Intracellular recordings were made from 103 neurones of the rat nucleus accumbens in vitro. 2. Dopamine (3-100 microM; in sulpiride, 1 microM) hyperpolarized neurones (79%) by acting at D1 receptors: dopamine (3-100 microM; in SCH23390, 1 microM) depolarized neurones (55%) by acting at D2 receptors. 5-Hydroxytryptamine (1-100 microM) depolarized 86% neurones. 3. Both actions of dopamine as well as the effect of 5-hydroxytryptamine were potentiated by cocaine (0.3-30 microM), which had no effect of its own on membrane potential. 4. Dose-ratio was computed as [(concentration of agonist causing a 4 mV potential change in cocaine)/(concentration of agonist causing a 4 mV potential change without cocaine)]. Cocaine (1-30 microM) caused the same dose-ratio whether dopamine depolarizations (D2) or hyperpolarizations (D1) were measured; the dose-ratio ranged from 2 (1 microM) to 50 (30 microM). 5. Responses to 5-hydroxytryptamine were increased more than responses to dopamine; cocaine 1 microM gave a dose-ratio of 13.4 and at 30 microM gave a dose-ratio of 118. 6. It is concluded that cocaine acts to inhibit the uptake of dopamine and 5-hydroxytryptamine in slices of rat nucleus accumbens; lower concentrations of cocaine (0.3 to 1 microM) are particularly effective in potentiating the action of 5-hydroxytryptamine.

Radioautographic method for quantifying regional monoamine innervations in the rat brain. Application to the cerebral cortex

Conditions leading to selective and complete labeling of the noradrenaline (NA) and serotonin (5-HT) innervations in rat cerebral cortex were sought by incubating 200-micron-thick whole hemisphere slices with various combinations of tritiated monoamines and uptake blockers at different concentrations in the presence of a monoamine oxidase inhibitor. After fixation with glutaraldehyde, post-fixation with osmium tetroxide and flat-embedding in Epon, 4-micron-thick sections of the entire slices were radioautographed by dipping in nuclear emulsion. As previously reported, dopamine (DA) terminals could be specifically visualized and counted following incubation with 1 micron [3H]DA and 5 microM desipramine (DMI) with or without 5 microM citalopram (CITAL). The number of NA terminals could thus be obtained by subtracting DA varicosities from the total number of sites labeled in adjacent slices incubated without DMI but in presence of CITAL to eliminate some interspecific labeling of 5-HT terminals. NA terminals could also be identified exclusively and counted after labeling with 1 microM [3H]NA in the presence of 10 microM benztropine. 5-HT terminals were specifically detected after incubation with 1 microM [3H]5-HT in the presence of 10 microM non-radioactive NA. The labeled varicosities were counted in areas FR1 and PAR1 of the frontal and the parietal neocortex, respectively, with the aid of a microcomputer-based image analysis system. DA varicosities were concentrated mainly in layer VI of these regions and were more numerous in the frontal than the parietal area. NA terminals were equally distributed in the two regions but approximately twice as numerous in layer I than subjacent layers. The 5-HT innervation also showed a comparable overall density in the two cortical regions but with a differing intracortical distribution. In the frontal area, 5-HT terminals were slightly more concentrated in layer I (1.3-fold) than underlying layers where they were rather uniformly distributed. In the parietal area, layer I was again the most densely innervated (1.8 times the average), but a second zone of higher density (1.5 times average) was present in the outer part of layer V. The remaining layers showed lower numbers of 5-HT terminals than in the frontal region. To obtain absolute estimates of these innervation densities, the number of detected varicosities was assessed experimentally as a function of radioautographic exposure time and of histological section thickness, and their 'equivalent circle diameter' was measured in electron microscope radioautographs.(ABSTRACT TRUNCATED AT 400 WORDS)

Free amino acid content of astroglial cell clones derived from 8-day postnatal mouse cerebella

We have measured the free amino acid content of three distinct astroglial cell clones derived from permanent lines obtained after "spontaneous immortalization" of 8-day postnatal mouse cerebellar cultures; these clones show characteristics similar to the Golgi Bergmann glia cells, the fibrous astrocytes, and the velate protoplasmic astrocytes, i.e., the three main types of cerebellar astrocytes. The relative concentrations of amino acids that are thought to act as neurotransmitters were compared in confluent cultures of the different astroglial clones. The most striking result was a high concentration of glycine (20% of free amino acids), even in astroglial cells cultured in a glycine-free medium, a finding suggesting that glycine is synthesized by the astroglial clones. Furthermore, no gamma-aminobutyric acid (GABA) was detected. In contrast, a "neuron-like" clone derived from the same cerebellar culture contained GABA, whereas its glycine content was much lower than that of the astroglial clones. The present results, together with our previous finding of glycine synthesis in an astrocytic clone derived from 14-day postnatal mouse cerebella transformed by simian virus 40, indicate that a high glycine content may be characteristic of many cerebellar astroglial types.

Amino acid and monoamine transport in primary astroglial cultures from defined brain regions

The uptake of L-[3H]glutamate, L-[3H]aspartate, gamma-[3H]aminobutyric acid (GABA), [3H]dopamine, DL-[3H]norepinephrine and [3H]5-hydroxytryptamine (5-HT) was studied in astrocytes cultured from the cerebral cortex, striatum and brain stem of newborn rat and grown for 2 weeks in primary cultures. The astrocytes exhibited a high-affinity L-glutamate uptake with Km values ranging from 11 to 110 microM. Vmax values were 4.5 in cerebral cortex, 39.1 in striatum, and 0.4 in brain stem, nmol per mg cell protein per min. There was a less prominent high-affinity uptake of L-aspartate with Km values from 88 to 187 microM. Vmax values were 7.4 in cerebral cortex, 37.1 in striatum, and 3.1 in brain stem, nmol per mg cell protein per min. The high-affinity GABA uptake exhibited Km values ranging from 5 to 17 microM and Vmax values were 0.01 for cerebral cortex, 0.04 for striatum, and 0.1 for brain stem, nmol per mg cell protein per min. No high-affinity, high-capacity uptake was found for the monoamines. The results demonstrate a heterogeneity among the astroglial cells cultivated from the different brain regions concerning the uptake capacity of amino acid neurotransmitters. Furthermore, amino acid transmitters and monoamines are taken up by the cells in different ways.

Characterization of sodium-dependent, high-affinity serotonin uptake in rat spinal cord synaptosomes

Synaptosomal accumulation of [3H]serotonin was used to determine if the rat spinal cord possesses a high-affinity neuronal uptake system for serotonin. Two temperature-dependent accumulation processes were found, one sodium-dependent, the second sodium-independent. Sodium-dependent [3H]serotonin accumulation was linear with sodium concentrations up to 143 mM, was associated with the purified synaptosomal fraction (P2B), and decreased 76% by osmotic lysis, 88% by sonication, and 96% by 0.1% Triton X-100. Drug inhibition studies demonstrated fluoxetine to be the most potent inhibitor of this system (IC50 0.075 microM) while desipramine (IC50 0.43 microM) and nomifensine (IC50 0.95 microM) were less potent. Kinetic analysis revealed that sodium-dependent accumulation in purified synaptosomes was saturable at low [3H]serotonin concentrations (Ku = 50 nM, Vmax = 4 pmol/mg protein/min). Sodium-independent [3H]5-HT accumulation was substantially less sensitive to fluoxetine, desipramine and nomifensine. While sodium-independent accumulation was not significantly affected by osmotic lysis, it was markedly increased by prior sonication of tissue. Also, in contrast to sodium-dependent accumulation, sodium-independent accumulation was evenly distributed in all tissue fractions, and was not saturable at low [3H]serotonin concentrations. It is concluded that sodium-dependent [3H]serotonin accumulation reflects uptake into spinal serotonergic nerve terminals while sodium-independent accumulation probably reflects a temperature-sensitive binding to membrane fragments. Comparison to brain uptake of serotonin and the necessity for using 37 degrees C sodium-free blanks rather than 0 degree C blanks in spinal cord homogenates is discussed.

Accumulation of putative amino acid neurotransmitters, monoamines and D-Ala2-Met-enkephalinamide in primary astroglial cultures from various brain areas, visualized by autoradiography

The accumulation of amino acids, monoamines and D-Ala2-Met-enkephalinamide (Enk) was visualized by autoradiography in astroglial primary cultures from different well-defined brain areas. The most prominent accumulation of grains was seen after incubating astroglial cultures from cerebral cortex, hippocampus and striatum with glutamate. Less uptake was seen in brainstem and cerebellar cultures. Similar results were found with aspartate but at a lower uptake level. The accumulation of GABA was moderate in all cultures studied. Dopamine, norepinephrine and 5-hydroxytryptamine (5-HT) showed only a slight accumulation and enkephaline did not accumulate at all. The results demonstrate that astroglial cells are not general inactivators for neurotransmitters, as monoamines are taken up only slightly and enkephalin not at all, while the cells have the capacity to accumulate at least some amino acid neurotransmitters. Furthermore, astroglial cells from different brain regions have different capacities to accumulate the various amino acid neurotransmitters supporting the view of regionally specialized astroglial cells.

Regulation of hippocampal sympathetic ingrowth: role of afferent input

Peripheral noradrenergic fibers from the superior cervical ganglion (SCG) appear in the hippocampal formation of the adult rat central nervous system following damage to the medial septal nucleus or its afferent fibers. The appearance of these fibers coincides with a significant and substantial increase in the concentration of norepinephrine in the dentate gyrus and in the ability of synaptosomes made from the dentate to take up [3H]norepinephrine (NE) in vitro. Up to 7 weeks following a medial septal lesion, dentate norepinephrine levels are significantly lower if the sympathetic preganglionic trunk has been sectioned at the time septal lesions are made. By contrast, the uptake of [3H]NE into dentate synaptosomes is not affected by the preganglionic section. Furthermore, if the sectioned preganglionic trunk is allowed to reinnervate the SCG, the dentate NE concentration rapidly returns to levels equivalent to dentates with intact sympathetic preganglionic trunks. In addition to the ingrowth of the sympathetic fibers, central noradrenergic fibers display a sprouting or 'pruning' response to medial septal lesions. These data show that afferent input regulates the neurotransmitter concentration during sympathetic ingrowth while retrograde influences from the target appear to regulate the density or extent of the growing fibers. The experimental findings are discussed in light of the hypothesis that the hippocampal formation is capable of producing a sympathetic growth factor following septal denervation.

Sprouting of noradrenergic fibers in hippocampus after medial septal lesions: contributions of the central and peripheral nervous systems

The neuronal sprouting of noradrenergic fibers was studied in the hippocampal formation. The extent and time course of lesion-induced plasticity of both central and peripheral noradrenergic neurons was determined by assaying norepinephrine (NE) concentrations and high-affinity [3H]NE uptake in the dentate gyrus at 2 to 16 weeks after medial septal lesions. Two weeks after a medial septal lesion there was a dramatic decrease in dentate NE. During the subsequent weeks normal concentrations of dentate NE were reestablished. The recovery or increase of NE with time reflected a contribution from both central and peripheral noradrenergic systems. Although both central and peripheral noradrenergic systems contributed to this recovery, they did so in very different ways. The time course of the central noradrenergic response was slower than that of the peripheral system and the final NE concentrations were quite different for the two systems. The central adrenergic system's sprouting response apparently stabilized when normal NE concentrations were attained, whereas the ingrowth of peripheral sympathetic fibers continued to concentrations that were well above normal unoperated levels. The findings have implications in relationship to the different possible controlling mechanisms governing neuronal plasticity of the central and peripheral noradrenergic systems.

Trh in the rat cerebellum: II. Uptake by cerebellar slices

We investigated the in vitro uptake of exogenous TRH by rat cerebellar slices. TRH was found to be taken up via a process sharing many of the properties of a high affinity transport system, viz: (1) saturation kinetics; (2) high affinity kinetic constants (Km1 = 1.06 X 10(-5) M, Km2 = 5.6 X 10(-6) M); (3) temperature sensitivity (Q10 = 1.48); (4) dependency on the sodium concentration in the incubation medium; and (5) tissue/medium ratios greater than 1. After 60 min of incubation at 27 degrees C in the presence of Bacitracin, the tissue/medium ratio was 5:1. Under these conditions 70% of the total label was recovered as [3H-Pro]TRH. These findings demonstrated the existence of removal mechanisms for TRH in the cerebellum and gave further support to the hypothesis that TRH plays a functional role removal mechanisms for TRH in the cerebellum and gave further support to the hypothesis that TRH plays a functional role in this extrahypothalamic brain region.

Effects of alpha-adrenoceptor-stimulating drugs on baroreceptor reflexes in conscious cats

The action of some alpha-adrenoceptor stimulating drugs with a central effect (clonidine, alpha-methyldopa, reserpine) on baroreceptor reflexes was studied in conscious cats (both in the resting condition and when influenced by emotional tension or electrical stimulation of the hypothalamus). The sedative effect of these drugs was observed simultaneously with bradycardia and the increase of baroreceptor reflexes. Clonidine and reserpine (in 6-24 h after injection) lowered blood pressure while alpha-methyldopa (40 mg/kg) increased it. Confrontation with a dog or electrical hypothalamic stimulation produced hypertensive reactions and diminished the baroreflexes. All drugs reduced the emotional and hypertensive reactions caused by natural stress situations and restored baroreceptor reflexes. On the other hand, neither clonidine nor alpha-methyldopa changed the decrease of baroreceptor reflexes caused by electrical hypothalamic stimulation. It is supposed that central alpha-adrenoceptor stimulating drugs do not influence processes of hypothalamic modulation of baroreceptor reflexes. The increase in baroreflex activity after clonidine, alpha-methyldopa and reserpine appears to be due to a direct effect of the drugs on the central neurones mediating baroreceptor reflexes and to the tranquillizing action of these drugs.

Selective retrograde labeling indicating the transmitter of neuronal pathways

A number of tritiated transmitter related compounds-amino acids and biogenic amines-were injected into the rat caudoputamen or substantia nigra in order to test (1) for the occurence of autoradiographic perikaryal labeling, (2) for a selectivity of perikaryal labeling relating certain compounds to certain pathways, and (3) for the relation of perikaryal labeling to known transmitter specificitites of the systems involved. Perikaryal labeling was observed after injection of some but not all of the substances used and was best explained by retrograde labeling in pathways projecting to the injection sites. Six hours after injection of high concentrations of tritiated transmitter into the terminal area, perikaryal labeling was observed: (A) in substantial nigra compacta (A9), A10 (rostral) and A8 (all heavy), and in n. raphe dorsalis (light) after [3H]-dopamine and [3H]-norepinephrine injection into caudoputamen; (B) same pattern as in A, but heavy in n. raphe dorsalis after [3H]-serotonin injection into caudoputamen; perikaryal labeling absent in cortex and thalamus after injection of substances mentioned in A and B; (C) only in substantia nigra compacta (minimally) after [3H]-GABA injection into caudoputamen; (D) in cerebral cortex and thalamus but not in substantia nigra, A10, A8, nor in n. raphe dorsalis after injection of [3H]-D-aspartate into caudoputamen; (E) in the rat caudoputamen but not in n. raphe dorsalis after [3H]-GABA injection into substantia nigra; (F) in n. raphe dorsalis but not in caudoputamen after [3H]-serotonin into substantia nigra. These results indicated, indeed, a certain selectivity-partly related to transmitter specificity-for perikaryal labeling patterns. As a method, transmitter specific retrograde tracing could be useful in pathways with dopamine-, serotonin-, and GABA-mediated synaptic transmission.

Biochemical characterization of [3H]norepinephrine uptake in dissociated brain cell cultures from chick embryos

The uptake of [3H]norepinephrine ([3H]NE) was studied in dissociated brain cell cultures prepared from 8-day-old chick embryos using the whole brain (minus optic lobes). Uptake [3H]NE, 5 x 10(-9) m, 10 min incubation, in freshly dissociated noncultured embryonic chick brain cells, was detected in 6-day-old embryos; it was temperature and drug (cocaine, metanephrine) sensitive and increased with brain development. In cultured cells, which were assayed at various days in culture, the increase in [3H]NE accumulation per culture was less than that seen in freshly dissociated noncultured embryonic cells. When [H]NE uptake was expressed per mg protein, a decrease with days in culture was observed. reflecting perhaps a dilution of growth or proliferation of cells not accumulating NE. Metanephrine, 5 X 10(-6) M, an inhibitor of extraneuronal uptake, inhibited [3H]NE in 5-day-old cultures whereas desmethylimipramine, an inhibitor of neuronal uptake, inhibited [3H]NE uptake in 15- and 20-day-old cultures. Cocaine, another neuronal inhibitor, inhibited [3N]NE at 10 and 15 days only. We interpret these findings to suggest that during early growth in culture most neuroblasts accumulate NE nonspecifically and, as neuronal maturation proceeds, NE accumulation becomes specific.

Concomitant development of [3H]-dopamine and [3H]-5-hydroxytryptamine uptake systems in rat brain regions

1 Synaptosomal uptake mechanisms of 5-hydroxytryptamine and dopamine were examined in cerebral cortex, corpus striatum and midbrain plus brainstem of developing rats. 2 In all regions, there was generally a parallel biphasic development of both uptake systems; the most rapid increases occurred in the first two weeks postpartum, followed by a slower rate of increase. 3 Kinetic studies with dopamine indicated that the maturation involved increases in maximal uptake without a change in the substrate Km, suggesting that there is a change in the number or terminals but not in the uptake system per se.

Identification of MSH release-inhibiting elements in the neurointermediate lobe of the rat

Neurointermediate lobes of rats comprise elements which, when excited in vitro, bring about an inhibition of the release of melanocyte stimulating hormone (MSH). Superfusion of neurointermediate lobes of intact donor rats with medium containing 45 mM K+ induced a stimulation of the release of oxytocin, arginine-vasopressin and dopamine (DA) and inhibited the release of MSH. Fluorescence histochemical observations and the results of release studies indicate that electrothermic lesions in the mediobasal hypothalamus induced a more rapid degeneration of dopaminergic than of peptidergic terminals in the neurointermediate lobe. Dopaminergic nerve terminals and the stimulated release of DA had vanished completely on the second day after these lesions, which coincided with the disappearance of K+-induced inhibition of MSH release. Frontal hypothalamic deafferentations resulted in disappearance of peptidergic nerve terminals as evidenced by the development of diabetes insipidus and the strong decline of depolarization-induced release of oxytocin and vasopressin from neurointermediate lobes in vitro. In contrast, the dopaminergic plexus was left intact, as was the K+-induced stimulation of DA release and inhibition of MSH release. We conclude that the K+-induced inhibition of MSH release is mediated by DA rather than by neuropeptides from terminals in the neurointermediate lobe. The results are in agreement with the proposed MSH release-inhibiting role of the dopaminergic tuberoinfundibular neurones.

Light and electron microscopic identification of monoaminergic terminals in the central nervous system

A brief critical survey of methods used for light and electron microscopic examination of amine-containing pathways within the CNS. Light microscopic techniques such as fluorescence histochemistry, immunocytochemistry, autoradiography, silver degeneration techniques, and retrograde tracing technique are suitable for studying the topography of pathways but, due to limits of resolution, they are inadequate for identifying terminals. Electron microscopy which is adequate to visualize terminals does not provide an overall view. This review considers various methods which have been devised to specifically detect aminergic nerve terminals. Electrolytic and chemical induced degenerations are described in noradrenergic, dopaminergic, and serotoninergic terminals. Although the individual degenerative alterations are not specific for aminergic terminals, the degenerative process when considered as a whole can be informative. At present no single technique can provide complete information about the origin, course, connections, and terminals of aminergic systems. Concurrent application of light and electron microscopy, experimental surgery, histochemistry, and microsample biochemistry would provide a complete description.

High-affinity GABA and glutamate transport in developing nerve ending particles

The high-affinity transport of [3H]GABA and [14C]glutamate was measured in discrete nerve ending fractions isolated from the developing rat cortex, beginning on day 7 postpartum and prepared using discontinuous Ficoll-isotonic sucrose gradients. On day 7 the material sedimenting in the lightest gradient fractions contained the highest density of particles capable of high-affinity transport. With increasing age, the transport sites became progressively associated with more dense particles in the gradient. On day 14, the Vmax values for both [3H]GABA and [14C-A1glutamate transport in the most dense nerve ending fraction were significantly increased over the adult value. This transient increase in the Vmax values disappeared by day 21. While the Km values for both transport systems were constant in all fractions for the adult animal, this was not the case in the developing pup. The Km values in the lightest fractions were significantly greater than those in the more dense fractions, suggesting that different transport systems may be present during development. Electron micrographs of the various fractions were prepared from 7-day and adult animals. These data illustrate that the lightest fractions of the '7-day' gradient are enriched in profiles similar to developing nerve endings. With development, these light fractions become infiltrated with myelin, the immature nerve ending profiles disappear, and the bulk of the nerve endings are found in more dense fractions.

Dopamine uptake in serotoninergic terminals in vitro: a valuable tool for the histochemical differentiation of catecholaminergic and serotoninergic terminals in rat cerebral structures

An in vitro method was developed to separately visualize dopaminergic, noradrenergic and serotoninergic terminals in the cerebral, hippocampal and cerebellar cortices of the rat, by means of the glyoxylic histochemical fluorescence method. Animals were pretreated with alpha-methylparatyrosine to deplete catecholamine stores. Thin vibratome sections were made and incubated in the presence of various exogenous amines and inhibitors of the catecholaminergic and serotoninergic transport systems. Experimental conditions insuring the best specificity were determined and the validity of the combined pharmacological and histochemical approach was further tested by using animals in which the cortical dopaminergic, noradrenergic or serotoninergic innervations were destroyed. Under the experimental conditions used, norepinephrine as well as alpha-methyl-norepinephrine were taken up in only noradrenergic and dopaminergic terminals. A separate visualization of the two systems was obtained by using specific uptake inhibitors. Dopamine was taken up not only in catecholaminergic but also in serotominergic terminals. The uptake of DA in serotoninergic fibers was inhibited by a specific inhibitor of the serotoninergic transport system or by the presence of serotonine in the incubating medium. The signification and the implications of thes results are discussed.

Electrically induced release of [3H]dopamine from slices obtained from different rat brain cortex regions. Evidence for a widespread dopaminergic innervation of the neocortex

Slices obtained from the deeper layers of the rat dorsal frontal, parietal and occipital brain cortex were incubated in vitro with 6.25 X 10-7 M [3H]dopamine (DA), and subsequently superfused and electrically stimulated, while held on quick transfer electrodes, and changes in the efflux of 3H and of the individual amines measured. The separation of the amines, with quantitative recoveries, was performed by chromatography on cation-exchange resins eluted sequentially with water, 1 N HCL AND 6 M urea i 1 N HCl. When no drugs were used, the prestimulation efflux was entirely formed by deaminated metabolites, while following stimulation there was an increase in the efflux of deaminated metabolites, and considerable amounts of [3H]-noradrenaline (NA) now appeared. No DA was present in the pre- or poststimulation medium. Similar results were obtained in all the regions studied. When the slices were incubated with 10-5 M desmethylimipramine (DMI), 10-4 Mnialamide and 10-4 M tropolone, before and during incubation with [3H]DA, it was observed that, prior to stimulation, the efflux was composed of deaminated metabolites, DA and 3-methoxytyramine (MTA), and following the electrical stimulus there was an increased release of DA, NA and deaminated compounds (in order of decreasing release), while no change in that of MTA was evident. The stimulus-induced release of DA was greatest from frontal slices, intermediate from parietal, and lowest from occipital ones. DMI-resistant uptake of [3H]DA also diminished when passing from frontal to occipital. These findings are interpreted as due to the presence of dopaminergic axon terminals in all the regions studied, but with a density that diminishes in a rostrocaudal direction.

Inhibition of [3H]norepinephrine uptake in peripheral organs of some mammalian species by ouabain

In order to demonstrate the possible involvement of (Na+ + K+)-ATPase in the high affinity uptake of [3H]-norepinephrine in the sympathetic nerve endings, the effect of ouabain on [3H]norepinephrine uptake in spleen and heart slices of five mammalian species was examined. The ouabain sensitivity of [3H]norepinephrine uptake in the heart slices form various species, as determined by the estimation of IC52, was, in increasing order, lamb (2,3 muM) less than calf (2.5 muM) less than guinea pig (4 muM) less than rabbit (10muM) less than rat (greater than 500 muM). The IC50 values in the spleen slices were: lamb (1 muM) less than calf (3.2 muM) less than rabbit (9.5 muM) less than guinea pig (25 muM) less than rat (greater than 500 muM). The IC50 values for the inhibition of specific [3H]ouabain binding in the microsomal fractions of spleen and heart of the five mammalian species by ouabain were similar to the IC50 values for the inhibition of [3H]norepinephrine uptake by the cardiac glycoside. Since ouabain is known to bind exclusively to (Na+ + K+)-ATPase of a microsomal fraction, these results suggest that the inhibition of [3H]norepinephrine uptake in the sympathetic nerve endings by ouabain is mediated by the inhibition of (Na+ + K+)-ATPase.

Effect of sympathomimetic amines on the synaptosomal transport of noradrenaline, dopamine and 5-hydroxytryptamine

The interaction of sympathomimetic amines with the transport of 3H-noradrenaline (3H-NE), 3H-dopamine (3H-DA) and 3H-5-hydroxytryptamine (3H-5-HT) were investigated in rat hypothalamic (3H-NE) and striatal (3H-DA) and 3 H-5-HT) synaptosomes. Modifications in the phenylethylamine structure led to changes in activity towards biogenic amine uptake and release: (a) the introduction of a beta-OH group led to compounds less active in inhibiting uptake and stimulating release of 3H-NE, 3H-DA and 3H-5-HT, with the exception of 3H-NE release which was stimulated more by unlabeled 1-NE than by DA; (b) the introduction of phenolic-OH groups always led to compounds which were stronger uptake inhibitors and releasers of the three biogenic amines; (c) the alpha-methylation increased the potency towards uptake inhibition and release stimulation, with the exception of 3H-NE release: in fact, the releasing activity of phenylethylamine was suppressed by alpha-methylation; (d) the introduction of a -Cl group in the para position selectively potentiated the effects on 3H-5-HT uptake and release and generally depressed those on catecholamine transport.

Partial separation of synaptosomes accumulating 4-aminobutyrate or glutamate by zonal centrifugation on a discontinuous sucrose gradient

Rat cerebral cortex slices were incubated with 1muM [3H]4-aminobutyrate or [3H]L-glutamine. The subcellular distribution of the accumulated labelled substances were determined by fractionating the nuclei-free homogenates on a 5-step discontinuous sucrose density gradient in a B XIV zonal rotor. The gradient was designed to separate the synaptosomes into 3 subpopulations of increasing density. The patterns of distribution of [3H]4-aminobutyrate and [3H-a1L-glutamate in the three synaptosomal peaks were distinctly different. This indicates the presence of separate types of nerve ending accumulating these two potential neurotransmitters, which are known to be metabolically closely linked through the enzyme glutamate decarboxylase. Recentrifugation of the 3 synaptosomal peaks on flat step gradients in a swingout rotor did not result in any further enrichment in transmitter-specific synaptosomes.